This invention relates generally to optical pulse compression and more particularly to noise reduction in fiber grating pulse compressor laser systems.
Optical pulse compression has become a standard laboratory technique because it offers increased time resolution as well as increased peak powers. While the addition of a pulse compressor to a mode-locked source provides great advantage, the pulse to pulse stability is often degraded.
Optical pulse compression techniques have been applied to a variety of mode-locked laser sources. Early work dealt with compression of Nd:glass and Helium-Neon lasers. More recently, attention has been focussed on dye lasers and continuous wave (cw) mode-locked Nd:YAG lasers. U.S. Pat. No. 4,646,308 to J. D. Kafka and T. M. Baer is directed to a synchronously pumped dye laser using ultrashort pump pulses formed by pulse compressing the output of a Nd:YAG laser. The compressed dye laser systems have provided the shortest pulses generated as well as ultrashort tunable pulses.
The compressed cw mode-locked Nd:YAG laser has been used in several applications. In electro-optic sampling in GaAs circuits, short synchronized infrared and visible pulses are required. The visible pulse, obtained by frequency doubling, is used to launch an electrical signal and the infrared pulse is used to probe the fields generated in the GaAs substrate. The compressed and frequency doubled output has been used to pump a dye laser producing tunable 200 fsec pulses with high average power. This source has also been used to perform ultrafast luminescence spectroscopy using sum frequency generation.
While the average power into the pulse compressor varies by a few percent (rms, 500 KHz bandwidth) and the average power out varies the same amount, the second harmonic of the compressed pulses can have much larger fluctuations. Several possible sources of these fluctuations including laser beam pointing, motion of the fiber and changes in the output polarization have been eliminated. Therefore, the additional noise on the second harmonic of the compressed pulses is predominantly due to fluctuations in the intensity and pulsewidth of the input pulses.